Diamond wire die with positioned opening

Abstract: A CVD diamond die for drawing wire has top and bottom surfaces and opposing portions of a peripheral side located in respective regions of larger diamond smaller diamond grains. An opening which extends through the body from the top surface to the bottom surface is suitable positioned intermediate the side portions.

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to diamond wire dies. BACKGROUND OF THE INVENTION Wires of metals such as tungsten, copper, iron, molybdenum, and stainless steel are produced by drawing the metals through diamond dies. Single crystal diamond dies are difficult to fabricate, tend to chip easily, easily cleave, and often fail catastrophically because of the extreme pressures involved during wire drawing. With reference to single crystal wire dies, it is reported in Properties and Applications of Diamond, Wilks et al, Butterworth-Heinemann Ltd 1991, pages 505-507: "The best choice of [crystallographic] direction is not too obvious because as the wire passes through the die its circumference is abrading the diamond on a whole 360° range of planes, and the rates of wear on these planes will be somewhat different. Hence, the originally circular hole will not only grow larger but will loose its shape. However, 〈110〉 directions offer the advantage that the wire is abrading the sides of the hole with {001} and {011} orientations in abrasion resistant directions." Diamond dies which avoid some of the problems attendant with natural diamonds of poorer quality comprise microporous masses compacted from tiny crystals of natural or synthesized diamonds or from crystals of diamond. The deficiencies of such polycrystalline hard masses, as indicated in U.S. patent 4,016,736, are due to the presence of micro-voids/pores and soft inclusions. These voids and inclusions can be more than 10 microns in diameter. The improvement of the patent utilizes a metal cemented carbide jacket as a source of flowable metal which fills the voids resulting in an improved wire die. European Patent Application 0 494 799 A1 describes a polycrystalline CVD diamond layer having a hole formed therethrough and mounted in a support. As set forth in column 2, lines 26-30, "The relatively random distribution of crystal orientations in the CVD diamond ensures more even wear during use of the insert." As set forth in column 3, lines 50-54, "The orientation of the diamond in the polycrystalline CVD diamond layer 10 may be such that most of the crystallites have a (111) crystallographic axis in the plane, i.e. parallel to the surfaces 14,16, of the layer 10. Other crystal orientations for CVD films are known. U.S. patent 5,110,579 to Anthony et al describes a transparent polycrystalline diamond film as illustrated in Figure 3A, substantially transparent columns of diamond crystals having a 〈110〉 orientation perpendicular to the base. Because of its high purity and uniform consistency, CVD diamond may be desirably used as compared to the more readily available and poor quality natural diamond. Because CVD diamond can be produced without attendant voids, it is often more desirable than polycrystalline diamond produced by high temperature and high pressure processes. However, further improvements in the structure of CVD wire drawing dies are desirable. Particularly, improvements in grain structure of CVD diamond wire die which tend to enhance wear and uniformity of wear are particularly desirable. BRIEF SUMMARY OF THE INVENTION Hence, it is desirable obtain a dense void-free CVD diamond wire die having a structure which provides for enhanced wear and uniformity of wear. In accordance with the present invention, there is provided a die for drawing wire of a predetermined diameter comprising a CVD diamond body of the type including a region of larger diamond grains and a region of smaller diamond grains and having a peripheral side surface and opposing top and bottom surfaces wherein at least one portion of said peripheral side surface is in a region of larger diamond grains and another opposing portion of said peripheral side surface is in a region of smaller diamond grains, an opening extends through said body from said top surface to said bottom surface intermediate said one portion of said peripheral side surface and said opposing portion of said side surface. The opening may be suitably positioned in a region of diamond grains having the desired size. In accordance with a preferred embodiment, the opening has a wire bearing portion of substantially circular cross-section determinative of the diameter of the wire and extending along an axis which is at an angle with respect to the growth direction of the diamond grains. Preferable, the axial direction of the opening or bore and the growth direction of the diamond grains are substantially perpendicular. The diamond grains have a preferred 〈110〉 orientation parallel to their growth direction. The grain growth direction or grain columnar direction is angular to the axial direction of the opening. Hence, a wire bearing portion may be desirably positioned. In one case, the wire bearing portion may be positioned to intersects a plurality of single diamond grains, and, in another case, positioned to be substantially entirely within a single grain. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of a diamond wire die; Figure 2 is an enlarged top-view of a portion of the wire die shown in Figure 1; and Figure 3 is a cross-sectional view of the wire die portion shown in Figure 2. DETAILED DESCRIPTION Figure 1 illustrates a diamond wire die 11 produced from a CVD diamond layer. Such dies are typically cut from a CVD diamond layer which has been separated from a growth substrate. This layer may be thinned to a preferred thickness. The major opposing surfaces of the die blank may be planarized and/or thinned to the desired surface finish by mechanical abrasion or by other means such as laser polishing, ion thinning, or other chemical methods. Preferably, conductive CVD diamond layers can be cut by electro-discharge machining, while insulating films can be cut with a laser to form discs, squares, or other symmetrical shapes. When used for wire drawing, the outer periphery of the die 11 is mounted in a support so as to resist axially aligned forces due to wire drawing. As shown in more detail in Figure 1, the wire die 11 includes an opening 12 aligned along an axis in a direction normal to spaced apart parallel flat surfaces 13 and 15. For purposes of description, surface 13 is hereinafter referred as the top surface and surface 15 is referred to as the bottom surface 15. The opening 12 is of an appropriate size which is determined by the desired size of the wire. The straight bore section 17 of opening 12 includes has a circular cross section which is determinative of the desired final diameter of the wire to be drawn. From the straight bore section 17, the opening 12 tapers outwardly at exit taper 19 toward the top surface 13 and at entrance taper 21 toward the bottom surface 15. The wire to be drawn initially passes through entrance taper 21 where an initial size reduction occurs prior to passing through the straight bore section 17 and exit taper 19. The entrance taper 21 extends for a greater distance along the axial direction than exit taper 19. Thus, the straight bore section 17 is closer to top surface 13 than to bottom surface 15. Entrance taper 21 includes a wide taper 25 opening onto the bottom surface 15 and narrow taper 23 extending between the straight bore 17 and the wider taper 25. The opening 12 may be suitably provided by first piercing a pilot hole with a laser and then utilizing a pin ultrasonically vibrated in conjunction with diamond grit slurry to abrade an opening 12 by techniques known in the art. Typical wire drawing dies have a disc-shape although square, hexagonal, octagonal, or other polygonal shapes may be used. Preferably, wire dies have a thickness of about 0.4-10 millimeters. The length measurement as in the case of a polygonal shape or the diameter measurement as in the case of a rounded shape, is preferably about 1-20 millimeters. Preferred thicknesses are from 0.3-10 millimeters with preferred lengths being 1-5 millimeters. The opening or hole 12 suitable for drawing wire typically has a diameter from 0.030 mm to 5.0 mm. Wire dies as prepared above, may be used to draw wire having desirable uniform properties. The wire die may contain more than one hole, and these holes may or may not be the same diameter and shape. A preferred technique for forming the diamond wire die substrate of the present invention is set forth in U.S. patent 5,110,579 to Anthony et al. According to the processes set forth in the patent, diamond is grown by chemical vapor deposition on a substrate such as molybdenum by a filament process. According to this process, an appropriate mixture such as set forth in the example is passed over a filament for an appropriate length of time to build up the substrate to a desired thickness and create a diamond film. As set forth in the patent, a preferred film is substantially transparent columns of diamond crystals having a 〈110〉 orientation perpendicular to the base. Grain boundaries between adjacent diamond crystals having hydrogen atoms saturating dangling carbon bonds is preferred wherein at least 50 percent of the carbon atoms are believed to be tetrahedral bonded based on Raman spectroscopy, infrared and X-ray analysis. It is also contemplated that H, F, Cl, O or other atoms may saturate dangling carbon atoms. The preferred film utilized in the present invention has the properties described above including, grain boundaries between adjacent diamond crystals preferably have hydrogen atoms saturating dangling carbon bonds as illustrated in the patent. The view as illustrated in Figure 2 of the polycrystalline diamond film in cross section further illustrates the substantially transparent columns of diamond crystals having a 〈110〉 orientation perpendicular to the axial direction of the opening 21. Figure 1 illustrates a portion of the peripheral side surface at 35 which extends therebetween normal to top surface 13 and bottom surface 15. If the wire die has a circular shape, portion 35 comprises a narrow section of the periphery. If the wire die 11, has a polygonal shape, portion 35 may be an entire side surface. The orientation is determined on the cutting of the die 11 from the diamond film. An opposing peripheral surface is illustrated at 37 in Figure 1. As illustrated in Figure 2, which is an enlarged top view of a portion of the wire die of Figure 1, reference number 45 corresponds to a region of smaller diamond grains which are adjacent side portion 35 and reference number 47 corresponds to a region of larger diamond grains which are adjacent side portion 37. The orientation of the diamond film is such that peripheral side portion 35 corresponds to the initial growth surface and side portion 37 corresponds to the surface exposed to the vapor deposition or the final surface. As illustrated in Figure 2, the opening 12 has an axis which is at an angle with respect to the growth direction of the diamond grains. Preferably, the axial direction of the wire-die bore and the growth direction of the columnar diamond grains, which have a a preferred 〈110〉 orientation parallel to their columnar direction (which is their growth direction), are substantially perpendicular. The diamond film is preferably positioned so that wire die peripheral surface 35 corresponds to the initial growth surface that was adjacent the molybdenum substrate during growth of the diamond film and peripheral surface 37 is the surface exposed to the chemical vapor deposition process. This positioning of the wire die results in a micro-graphic structure as illustrated in Figure 3 wherein the opening 12 is positioned in a region of diamond grains having a size intermediate the diamond grains of the initial growth region 45 and of the final growth region 47. The initial vapor deposition of diamond on the substrate results in the seeding of diamond grains or individual diamond crystals. As shown in Figure 2,the growth direction or columnar direction of the individual crystals is in an axial direction, i.e. a direction normal to the respective peripheral portions 35 and 37 and substantially parallel to the top and bottom surfaces, 13 and 15, the cross sectional area as measured along planes parallel to the respective peripheral portions 45 and 47 proceeding from surface 45 towards surface 47 and substantially parallel to the top and bottom surfaces, 13 and 15. The cross sectional area of the crystals as measured along the planes parallel to the respective peripheral portions 45 and 47 increases along the grain growth direction. Figure 2, shows view of the top surface 13 where a portion of the diamond grains are at their intermediate width. Hence, as previously mentioned, it is possible to select the position of the straight bore section. As mentioned above and as shown in the drawings, the straight bore section 17 is positioned in a location of diamond crystals of intermediate width. In accordance with another embodiment of the present invention, the straight bore section 17 may be positioned with the smaller grain region of the substrate so the bore section 17 is substantially entirely within a plurality of diamond grains. As illustrated in Figure 3, the straight bore 17 is positioned interior to plurality of diamond grains 27. It is also contemplated that the straight bore section 17 be positioned within a single diamond grain. This would require examination of the crystal structure so as to suitably position the straight bore section 17. The 〈110〉 preferred grain direction is preferably perpendicular to the major plane of the film and is randomly aligned about the 〈110〉 direction. In Figure 3, the 〈110〉 growth direction of the diamond grains is parallel to the top surface 13 and the bottom surface 15 of the die and perpendicular to the axial direction of the bore 12 of the die. Do to enhanced wear and cracking resistance when used as a wire die, non-opaque or transparent or translucent CVD diamond is preferred. A preferred process for making the film is the filament process as above described. Additional preferred properties of the diamond film include a thermal conductivity greater than about 4 watts/cm-K. Such wire dies have a enhanced wear resistance and cracking resistance which increases with increasing thermal conductivity. The film is preferably non-opaque or transparent or translucent and contains hydrogen and oxygen greater than about 1 part per million. The diamond film may contain impurities and intentional additives. Impurities may be in the form of catalyst material, such as iron, nickel, or cobalt. Diamond deposition on substrates made of Si, Ge, Nb, V, Ta, Mo, W, Ti, Zr or Hf results in CVD diamond wire die blanks that are more free of defects such as cracks than other substrates. By neutron activation analysis, we have found that small amounts of these substrate materials are incorporated into the CVD diamond films made on these substrates. Hence, the film may contain greater than 10 parts per billion and less than 10 parts per million of Si, Ge, Nb, V, Ta, Mo, W, Ti, Zr or Hf. Additionally, the film may contain more than one part per million of a halogen, i.e. fluorine, chlorine, bromine, or iodine. Additional additives may include N, B, O, and P which may be present in the form of intentional additives. It's anticipated that films that can be utilized in the present invention may be made by other processes, such as by microwave diamond forming processes. It is contemplated that CVD diamond having such preferred conductivity may be produced by other techniques such as microwave CVD and DC jet CVD. Intentional additives may include N, S, Ge, Al, and P, each at levels less than 100 ppm. It is contemplated that suitable films may be produced at greater levels. Lower levels of impurities tend to favor desirable wire die properties of toughness and wear resistance. The most preferred films contain less than 5 parts per million and preferably less than 1 part per million impurities and intentional additives.

Claims: A die for drawing wire of a predetermined diameter comprising a CVD diamond body characterised in that said body being of the type including a region of larger diamond grains and a region of smaller diamond grains, said die having a peripheral side surface and opposing top and bottom surfaces wherein at least one portion of said peripheral side surface is in a region of larger diamond grains and another opposing portion of said peripheral side surface is in a region of smaller diamond grains, an opening extends through said body from said top surface to said bottom surface intermediate said one portion of said peripheral side surface and said opposing portion of said side surface. A die for drawing wire in accordance with claim 1 wherein said one portion of a peripheral side surface corresponds to an initial diamond growth surface. A die for drawing wire in accordance with claim 1 wherein said opening extends entirely through said body along an axial direction from said top surface to said bottom surface orientation extending at an angle to said axial direction. A die for drawing wire in accordance with claim 3 wherein said wire bearing portion comprises a straight bore section having a circular cross section. A die for drawing wire in accordance with claim 3 wherein said opening tapers outwardly in one direction from said straight bore section toward said top surface and tapers outwardly in the opposite direction toward said bottom surfaces. A die for drawing wire in accordance with claim 5 wherein said outward taper in said one direction forms a exit taper for the wire and said outward taper in the other direction toward said bottom surface forms an entrance taper. A die for drawing wire in accordance with claim 6 wherein said entrance taper extends for a greater distance along the axial direction than exit taper. A die for drawing wire in accordance with claim 1 wherein said body has a thickness as measured from one surface to the other surface of about 0.3-10 millimeters. A die for drawing wire in accordance with claim 1 wherein said diamond is grown by chemical vapor deposition on a substrate consisting of Si, Ge, Mo, Nb, V, Ta, W, Ti, Zr or Hf or alloys thereof. A die for drawing wire in accordance with claim 1 wherein said diamond comprises a film of substantially transparent columns of diamond crystals having a 〈110〉 orientation at an angle to the axial direction of said opening.

Inventors: ANTHONY THOMAS RICHARD, WILLIAMS BRADLEY EARL, ANTHONY, THOMAS RICHARD, WILLIAMS, BRADLEY EARL
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1994
Main classification: B21C3
IPC codes: B21C3, C23C16